1. Field of the Invention
The present invention relates to power consumption reduction. More specifically, the present invention discloses an improved pulse width modulation controller with normal mode and green mode operation that increases the efficiency of the power supply and lowers power dissipation during relatively light load or no load conditions.
2. Description of the Prior Art
A main component of a switching mode power converter is the pulse width modulation controller. During normal operation, the controller drives the power converter at a fixed frequency. However, conventional power converters waste power during light load or no load conditions since the controller continues driving the power converter at the fixed frequency regardless of the load. At light load the power delivered to the load is “light” while the energy used to deliver the power remains about the same, thus its efficiency drops significantly in light or no load. In order to overcome this problem, green power supplies were created.
Green power supplies are power converters that reduce power consumption during light and standby modes. Commonly, this is achieved using burst mode operation or switching frequency reduction under light load or no load conditions.
In burst mode, the PWM driver sends a number of pulses depending on the load. For heavier loads more pulses are sent and for lighter loads fewer pulses are sent.
In a green power supply utilizing frequency change, the controller changes the switching frequency to a low value thereby reducing losses related to switching. This increases the efficiency of the power supply. With this type of controller the frequency of the drive signal changes while the ON time of the pulse remains constant, sometimes known as Constant ON control.
However, it can be difficult to design circuitry that provides smooth transitions between normal mode and green mode.
Additionally, in low power applications, the efficiency of the power supply becomes critical.
Therefore, there is need for an improved pulse width modulation controller that smoothly transitions between normal mode and green mode in order to increase the efficiency of the power supply and lowers power dissipation during light load or no load conditions.